This invention relates generally to optical communication devices. More particularly, this invention relates to a low power optical transceiver for use in portable computers, calculators and other devices to send and receive a data stream across greater distances and at higher data communication rates than has been previously possible.
Communicating information optically between two devices has distinct advantages over the more conventional technique of using a physical connection such as a cable. Optical communication is more convenient because it does not require the presence of a cable nor the effort to connect the two devices together. Moreover, optical communication does not suffer from electromagnetic radiated noise or provide a path for destructive electrostatic discharge (ESD) as in the case of wires.
Optical transceivers (devices which can both transmit and receive optical communications) have been successfully incorporated into a number of portable computing devices for communicating data between such devices and others such as computers and printers. U.S. Pat. No. 5,075,792, for example, describes a low power optical transceiver for use in portable computing devices such as hand-held calculators. A similar optical transceiver, but using a photo diode instead of a photo transistor, is incorporated into the HP95LX palm-top computer from Hewlett-Packard Company.
However, these optical transceivers and others in the prior art have inherent limitations in their range and transmission rates. Typically, such transceivers can transmit only three to ten inches (7.6 to 25 cm) at a fixed, relatively low baud rate such as 2400 baud. (The baud rate is the number of signalling units per second. In many cases, the baud rate is equivalent to the number of bits per second.) Their limited range affects the convenience of use, and the low baud rate increases the time and power required to transmit data. Moreover, the fixed baud rate may render an optical transceiver incompatible with newer devices that operate at different transmission rates.